Mounting structures for electrical devices have met increasing demands for strength and stability with the advent and common installation of ceiling fans, particularly lighted such devices, and large chandeliers. While each of these electrical fixtures or devices has its own unique set of mounting problems, ceiling fans with their large heavy motors and often the addition of lighting devices, have posed a particular issue because of the large static loads which they represent when hung from a ceiling. Additionally, the fan rotation provides a dynamic load that also requires consideration when mounting such devices.
There have been numerous efforts in the prior art to provide adequate structure for the hanging or mounting of large electrical devices that represent large static and/or dynamic loads.
U.S. Pat. No. 4,892,211 to Jorgensen describes a ceiling box for mounting and supporting a ceiling fan on a ceiling. The ceiling box includes a top wall portion with a side wall portion surrounding the periphery of the top wall portion. The box is open at the end opposite the top wall portion and the side wall portion has a pair of flanges extending normal thereto into the open end of the box. These flanges have holes in them for receiving fan-supporting screws. In a first embodiment, a pair of threaded mounting screw holes are formed in the top wall portion and are each axially aligned with an unthreaded hole that extends through the respective flange. In a second embodiment, the holes in the flanges are also threaded for added support.
U.S. Pat. No. 5,183,233 to LaPalomento, describes a support for hanging an electrical fixture from a ceiling or wall and a method for suspending the fixture. The support comprises a panel that is intended to be affixed to the grid work of a house and a support affixed to the panel that holds the electrical fixture. A slot is provided on the rear of the panel to hold the panel flush against a flat surface and to allow electrical wiring to connect to the electrical fixture.
U.S. Pat. No. 5,234,119 to Jorgensen et al, describes a plastic ceiling box adapted to support a ceiling fan and designed to be mounted on a structural member, such as a ceiling joist. The ceiling box comprises a body member having a lower wall and a pair of sidewalls defining a recess for snugly receiving a ceiling joist. Box mounting holes for receiving box mounting fasteners are located at opposite sides and ends of the lower wall for attaching the ceiling box to the joist. Openings for receiving fan supporting fasteners are formed in the body member adjacent the box member and aid in attaching the body member to the joist. This overall arrangement provides sufficient support and strength to resist dynamic loads imposed by the ceiling fan even though the ceiling box is made of plastic.
U.S. Pat. No. 5,522,577 to Roesch describes a mounting assembly for supporting a ceiling fan that includes a support beam located inwardly of the ceiling surface a predetermined distance. An electrical box having a bottom wall is directly joined to and supported from the support beam. The box has sidewalls extending from the bottom wall through the ceiling substantially to the exposed ceiling surface and terminating in an open end. A rigid metal plate or disk member adapted for supporting and mounting a ceiling fan is positioned over the open end of the box. The disk member is of a size sufficient to have a peripheral portion extending radially beyond the side walls of the box and a plurality of mounting screws extend from the metal disk member through the interior of the box into connected engagement with the beam. The mounting screws support the disk member from the beam without reliance on the electrical box for support.
U.S. patent application Ser. No. 08/927,614 entitled "Ceiling Medallion Assembly" filed Sep. 11, 1997 in the name of Thomas J. Gretz describes a mounting assembly for holding an electrical device in place on a joist or stud. The assembly includes an electrical box having a planar base, preferably with three planar surfaces of different depths, a fastener device for temporarily securing an electrical box in place, a ceiling medallion for covering the electrical box, a second fastener device for temporarily securing the ceiling medallion to the electrical box and a fixation device for securely fastening the electrical box and a ceiling bezel to the joist or stud. The electrical box for mounting on the joist or stud includes: a generally rectangular housing with two opposite sides having a stepped appearance defining three different depths of the housing with a third side at a first shallow depth and a fourth side at a third deepest depth, a first back piece spanning the opposing sides at a first depth approximately equal to the thickness of the ceiling material, a second back piece spanning the opposites sides of the second depth that is greater than the first depth of the first back piece, the second depth being approximately equal to twice the thickness of the ceiling material and a third back piece spanning the opposite sides at a third depth that is greater than the second depth of the second back piece.
Although the foregoing methods and apparatus have all attempted to solve the problem of adequately mounting the increased loads of electrical fixtures, particularly fans, that place significant stresses upon the mounting structure as they rotate none provides for more than screw-type attachment of the electrical box to the rafter or other supporting structure. It would therefore be desirable to provide an electrical fan mounting assembly that because of its design and attachment scheme resists lateral movement that can result in loosening of the mounting screws.